Malaria, particularly disease caused by Plasmodium falciparum, remains one of the world's major health problems. As available chemotherapy for malaria is inadequate, an important need is the improvement in our understanding of the biology of P. falciparum so that new targets for antimalarial chemotherapy can be identified. Asexual malaria parasites degrade host erythrocyte hemoglobin to provide free amino acids for parasite protein synthesis. This unique metabolic process appears to be necessary for normal parasite development. We have shown that cysteine proteinase activity is required for malarial hemoglobin degradation, and we have identified, characterized, cloned, and expressed a Plasmodium falciparum trophozoite cysteine proteinase (TCP) that is a potent hemoglobinase. This project will involve the characterization of the biochemical properties and the biological role of TCP so as to test the hypothesis that this proteinase is required for the degradation of hemoglobin. We will characterize the kinetic properties, substrate specificity, glycosylation, intracellular trafficking, and processing of TCP. These studies will provide important information regarding the mechanism of action of TCP, and may identify new chemotherapeutic targets independent of the direct inhibition of enzyme activity. To directly test our hypothesis, we will characterize the sequential degradation of hemoglobin by TCP and other proteinases in vitro and in cultured parasites. We will also study the hydrolysis of globin by mutant TCPs with alterations of catalytically important amino acids and we will study the hydrolysis of mutant hemoglobins, acquired from patients with hemoglobinopathies or by recombinant DNA techniques. Our studies will definitively determine whether TCP is required for hemoglobin degradation, and should begin to define the specific roles of TCP and other proteinases in the complete hydrolysis of globin.